Integrated circuit technology continues to rapidly advance, with many circuit technologies being implemented using semiconductor fabrication processes. A variety of electrically conducting material is available for implementing the layers in the gates of semiconductor integrated circuits.
As well known in the art, silicon oxide film has been mainly used as a material of a gate insulating film in MOSFETs, and a polysilicon film has been used as a material of the gate. However, as the integration level of the semiconductor devices becomes higher, it is required that the line width of the gate and the thickness of the gate insulating film be reduced. In the case where a silicon oxide film is used as the material of the gate insulating film, if the thickness of the gate insulating film is too thin, the insulating characteristic is not stable, as the leakage current due to a direct tunneling through the gate insulating film becomes greater. Recently there has been an effort to use a high dielectric constant material, having a relatively higher dielectric constant than a silicon oxide film, as the material of the gate insulating film. Also, in order to minimize the polysilicon gate depletion effect, there has been an effort to use a metal gate instead of the polysilicon gate.
N-Metal films such as TaSix appear to be useful as N-metals. However, in some applications, a lower work function may be needed than that of a pure deposited TaSix film. Therefore, there is a need to provide methods of tuning the work function of a TaSix film to better suit NMOS applications.